[PowerPC] Treat 'Z' inline asm constraint as a true memory constraint

We currently emit incorrect codegen for this constraint because we set it as a
constraint that allows registers. This will cause the value to be copied to the
stack and that address to be passed as the address. This is not what we want.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=42762

Differential revision: https://reviews.llvm.org/D77542

Author: nemanjai

clang/lib/Basic/Targets/PPC.h

@@ -276,11 +276,12 @@ class LLVM_LIBRARY_VISIBILITY PPCTargetInfo : public TargetInfo {
       break;
     case 'Q': // Memory operand that is an offset from a register (it is
               // usually better to use `m' or `es' in asm statements)
+      Info.setAllowsRegister();
+      LLVM_FALLTHROUGH;
     case 'Z': // Memory operand that is an indexed or indirect from a
               // register (it is usually better to use `m' or `es' in
               // asm statements)
       Info.setAllowsMemory();
-      Info.setAllowsRegister();
       break;
     case 'R': // AIX TOC entry
     case 'a': // Address operand that is an indexed or indirect from a

clang/test/CodeGen/ppc64-inline-asm.c

@@ -37,3 +37,16 @@ double test_fmax(double x, double y) {
 // CHECK-LABEL: double @test_fmax(double %x, double %y)
 // CHECK: call double asm "xsmaxdp ${0:x}, ${1:x}, ${2:x}", "=^ws,^ws,^ws"(double %x, double %y)
 }
+
+void testZ(void *addr) {
+  asm volatile ("dcbz %y0\n" :: "Z"(*(unsigned char *)addr) : "memory");
+// CHECK-LABEL: void @testZ(i8* %addr)
+// CHECK: call void asm sideeffect "dcbz ${0:y}\0A", "*Z,~{memory}"(i8* %addr)
+}
+
+void testZwOff(void *addr, long long off) {
+  asm volatile ("dcbz %y0\n" :: "Z"(*(unsigned char *)(addr + off)) : "memory");
+// CHECK-LABEL: void @testZwOff(i8* %addr, i64 %off)
+// CHECK: %[[VAL:[^ ]+]] = getelementptr i8, i8* %addr, i64 %off
+// CHECK: call void asm sideeffect "dcbz ${0:y}\0A", "*Z,~{memory}"(i8* %[[VAL]])
+}